This invention relates to an electronically controlled automatic transmission in which, when a vehicle equipped with the transmission is to be propelled forward from rest on a road surface exhibiting a low coefficient of friction as caused by snow or the like, the mode in which the vehicle is to be started moving forward can be set, and in which the set mode is capable of being cancelled automatically.
When a vehicle having an automatic transmission is at rest on a road surface with a low coefficient of friction and the vehicle is to be propelled forward while in this state, the vehicle may become stuck in place since the transmission is fixed in the first speed range and cannot be shifted to second or third gear, as in the manner of an automatic transmission, to allow forward movement in these other gears. In an attempt to solve this problem in the prior art, a travel pattern selection switch is provided for manipulation by the driver in a certain limited range of the automatic transmission, such as the second speed range. By operating the switch when the transmission is in this speed range, the driver can select a second-gear or third-gear mode in which the vehicle can be started off from rest on the aforementioned slippery road surface.
With this conventional expedient, however, in order to select, say, the second-gear mode by the travel pattern selection switch, first the shift lever must be placed in a range (e.g. the second speed range) other than the range used in ordinary traveling (e.g. the D range), and then the travel pattern selection switch must be switched over by the driver. Such an operation is troublesome for the driver to perform. Furthermore, if the driver wishes to travel in the ordinary traveling mode (e.g. an economy mode) such as in third gear or fourth gear once the vehicle has been started off in second gear by use of the aforementioned switch, the driver must move the shift lever to another range each time and then must switch over the travel pattern selection switch. This is also a troublesome task for the driver to carry out.